A typical alternating-current surface discharge panel used as a plasma display panel (hereinafter, simply referred to as “panel”) has a large number of discharge cells that are formed between a front plate and a rear plate facing each other. The front plate has the following elements:                a plurality of display electrode pairs, each formed of a scan electrode and a sustain electrode, disposed on a front glass substrate parallel to each other; and        a dielectric layer and a protective layer formed so as to cover the display electrode pairs. The rear plate has the following elements:        a plurality of parallel data electrodes formed on a rear glass substrate;        a dielectric layer formed so as to cover the data electrodes;        a plurality of barrier ribs formed on the dielectric layer parallel to the data electrodes; and        phosphor layers formed on the surface of the dielectric layer and on the side faces of the barrier ribs.        
The front plate and the rear plate face each other such that the display electrode pairs and the data electrodes three-dimensionally intersect, and are sealed together. A discharge gas containing xenon in a partial pressure ratio of 5%, for example, is sealed into the inside discharge space. Discharge cells are formed in portions where the display electrode pairs face the data electrodes. In a panel having such a structure, gas discharge generates ultraviolet light in each discharge cell. This ultraviolet light excites the red (R), green (G), and blue (G) phosphors so that the phosphors emit the corresponding colors for color display.
As a driving method for the panel, a subfield method is typically used. In the subfield method, one field period is divided into a plurality of subfields, and gradations are displayed by the combination of the subfields where light is emitted.
Each subfield has an initializing period, an address period, and a sustain period. In the initializing period, an initializing waveform is applied to the respective scan electrodes so as to cause an initializing discharge in the respective discharge cells. This initializing discharge forms wall charge necessary for the subsequent address operation in the respective discharge cells and generates priming particles (excitation particles for causing an address discharge) for stably causing the address discharge.
In the address period, a scan pulse is sequentially applied to the scan electrodes (hereinafter, this operation being also referred to as “scanning”). Further, an address pulse corresponding to a signal of an image to be displayed is selectively applied to the data electrodes (hereinafter, these operations being also generically referred to as “addressing”). Thus, an address discharge is selectively caused between the scan electrodes and the data electrodes so as to selectively form wall charge.
In the sustain period, a sustain pulse is alternately applied to display electrode pairs, each formed of a scan electrode and a sustain electrode, at a predetermined number of times corresponding to a luminance to be displayed. Thereby, a sustain discharge is selectively caused in the discharge cells where the address discharge has formed wall charge, and thus causes light emission in the discharge cells (hereinafter, causing light emission in a discharge cell being also referred to as “lighting”, causing no light emission in a discharge cell as “non-lighting”). In this manner, an image is displayed in the display area of the panel.
In this subfield method, the following operations, for example, can minimize the light emission unrelated to gradation display and thus improve the contrast ratio. In the initializing period of one subfield among a plurality of subfields, an all-cell initializing operation for causing a discharge in all the discharge cells is performed. In the initializing periods of the other subfields, a selective initializing operation for causing an initializing discharge selectively in the discharge cells having undergone a sustain discharge is performed.
With a recent increase in the screen size and definition of a panel, the plasma display device is requested to have enhanced image display quality. However, a difference in drive impedance between display electrode pairs causes a difference in the voltage drop in drive voltage. This can produce a difference in emission luminance, even with image signals having an equal luminance, in some cases.
To address this problem, the following technique is disclosed (see Patent Literature 1, for example). In this technique, the lighting patterns in the subfields in one field are changed when the drive impedance changes between display electrode pairs.
The important factors in determining an image display quality include the brightness of a display image. The brightness of a display image is one of the important factors in determining the image display quality. Depending on the viewing environment of the plasma display device, a decrease in the luminance of a display image can be recognized as a deterioration of the image display quality in some cases.
In a generally-viewed dynamic image, e.g. a television broadcast, a steadily gazed portion, e.g. a human face, is relatively frequently positioned in the vicinity of the center of the image display surface (hereinafter, also simply referred to as “display surface”) of a panel. For this reason, the brightness of the central portion of the display surface is likely to be recognized as the brightness of the display image. Thus, when the central portion of the display surface has a low luminance, the user may have an impression that the display image is dark.
However, with the technique disclosed in Patent Literature 1, it is difficult to control the luminance of the discharge cells according to the positions on the display surface.